The 2008 Memorial Day Weekend tornado outbreak will continue to hammer the U.S. today, even as residents from Iowa and Minnesota clean up from the devastating tornadoes that killed eight people Sunday afternoon. A mile-wide tornado plowed through Parkersburg, Iowa between 5pm and 6pm CDT yesterday, killing five people in that city, and two in nearby New Hartford. It was the deadliest tornado in Iowa in more than 40 years. The tornado passed just north of the airport in Waterloo, Iowa, which recorded sustained winds of 64mph, gusting to 94 mph at 5:37pm CDT. Damage appeared to be at least EF-4 in photos I saw, and possibly EF-5 (over 200 mph). In Minnesota, another powerful twister killed at least one person and injured 9 in the Minneapolis suburb of Hugo.

Figure 1. Satellite image of the supercell thunderstorms that spawned the Parkerburg, Iowa and Hugo, Minnesota tornadoes on May 25, 2008.

The slow-moving low pressure system responsible for all the mayhem began in Colorado on Thursday, when the Storm Prediction Center (SPC) recorded 48 reports of tornadoes, including the EF-3 mile-wide twister that killed one person in Windsor, Colorado. On Friday, an additional 63 tornado reports occurred, mostly in Kansas. The tornado that hit Quinter, Kansas on Friday was the eighth violent EF-4 tornado of the year. Also on Friday, two people were killed in Cairo, Kansas when a tornado smashed a car trying to flee the storm. If you want to see why one should not try to escape a tornado in a car, take a look at what the tornado did to the car. Saturday was relatively quiet, with only 13 tornado reports, but Sunday's tally of 43 brought the 4-day total from the 2008 Memorial Day weekend outbreak to a remarkable 157 tornado reports. Some of these tornado reports are undoubtedly of the same tornado, so the actual number of tornadoes for the 4-day outbreak may be less than 150. BBC has some awesome aerial footage of the weekend tornadoes.

Figure 2. Radar reflectivity image (top) of the May 25, 2008 Parkersburg, Iowa tornado. The position of Parkersburg is marked by a circle with a cross in the middle. Bottom: Doppler velocity image of the tornado, showing a small core of red and blue colors right next to each other, denoting strong winds towards and away from the radar, the classic signature of a tornado vortex.

Figure 3. Radar reflectivity image (top) of the May 25, 2008 Hugo, Minnesota tornado. The position of Hugo is marked by a circle with a cross in the middle. Bottom: Doppler velocity image of the tornado, showing a small core of red and blue colors right next to each other, denoting strong winds towards and away from the radar, the classic signature of a tornado vortex. We've also saved a 12-frame radar animation of the Hugo cell, thanks to wunderground member Todd S.

Tallying up the numbersThe death toll from Sunday pushes this year's tornado deaths to 111, the most since 1998, when 130 were recorded. Assuming that the Parkersburg, Iowa tornado was an EF-4 or EF-5, there have been nine violent EF-4 or EF-5 tornadoes this year. This is the most since 1999, when 13 such twisters were recorded. The total number of tornadoes this year is approaching 1100, and we may challenge the all time record for tornadoes in a year of 1817, set in 2004. Could this be a sign of climate change? No, I don't think so, and I'll explain why in a blog later this week.

Severe weather forecastSevere weather will pound the U.S. again this Memorial Day, with the main action expected to stretch more than halfway across the country--from Texas to New York. NOAA's Storm Prediction Center has placed much of Kansas, Oklahoma, and the Texas Panhandle under its "Moderate Risk" category for severe weather, one step below its highest level of concern, "High Risk". Yesterday was also a "Moderate Risk" day in Iowa and Minnesota. The Weather Underground Severe Weather page and Tornado page are good places to go to follow the severe weather. Also, tune in to the chase accounts and awesome storm photos from Wunderblogger Mike Theiss. After today, it appears the severe weather outbreak will finally diminish, with only a slight risk of severe weather expected Tuesday, and no severe weather expected Wednesday.

Possible development in the Western Caribbean or Eastern Pacific late this weekFor the past 3-6 days, our most reliable global computer weather forecast models have been predicting the development of a low pressure system near or over Central America by Friday of this week. Given the persistence in the models in developing this low, we need to be alert to the possibility of a tropical depression forming in either the Western Caribbean or Eastern Pacific, on either side of Costa Rica and Nicaragua. It is uncertain which ocean basin such a storm might form in, and whether or not there will be a tropical wave around to help kick off development. It may be that the low pressure region will stay anchored over land south of the Yucatan Peninsula, preventing any development. This is the solution preferred by the ECMWF model in its last few runs. However, the GFS, NOGAPS, and Canadian models all predict a tropical depression might form in the Western Caribbean near Mexico's Yucatan Peninsula. In contrast, the UKMET shows development in the Eastern Pacific, on the Pacific side of Central America. Climatologically, May tropical storms are much more common in the Eastern Pacific than the Western Caribbean, so we should not discount the UKMET solution, even though it is an outlier. All five models predict that the Central American low pressure area will move northward towards the Gulf of Mexico, and wind shear may fall enough to allow a tropical depression to form should the low's center emerge over water. I'll be posting daily updates on the situation this week.

These are pictures taken of the storm that went through Forest Lake / Hugo, MN. The tornado passed 3 miles south of us, but we got a pretty vicious shot of hail for about 15 minutes straight. The pictures of bldg damage are west of the worst tornado damage, probably where the funnel cloud was just about to reach the ground.

THE FORECAST FOR THE EXTENDED PERIOD SUNDAY AND BEYOND IS RATHER LOWCONFIDENCE. THE GFS HAS BEEN INSISTENT ON BRINGING SOMETHINGTROPICAL LOOKING INTO THE NORTHWEST CARIBBEAN ON MONDAY.HOWEVER...THE LAST COUPLE OF RUNS OF THE EURO THROUGH THE 25/12ZWERE MUCH WEAKER AND FURTHER SOUTH AND WEST...ESSENTIALLY OVERMEXICO AND GUATEMALA. GIVEN THE FAR TIME RANGE AND DISAGREEMENTBETWEEN THESE TWO MODELS...WILL NOT INDICATE INCREASING WINDS ANDCLOUD COVER THAT THE GFS BRINGS BY THE END OF THE PERIOD.INSTEAD...WILL FOLLOW A FORECAST CLOSER TO CLIMO FOR EARLY JUNE.

LONG TERM (WEDNESDAY NIGHT-MONDAY)...THE MAIN FEATURE IN THEMODELS CONTINUES TO BE THE AREA OF LOW PRESSURE THAT MANY DIFFERENTMODELS ARE FORECASTING TO DEVELOP OVER THE SOUTHWESTERN CARIBBEANSEA. THIS LOW ORIGINATES OVER THE EASTERN PACIFIC...THEN CROSSESINTO THE CARIBBEAN. NORMALLY...TROPICAL DEVELOPMENT WOULD BE QUITESLOW DUE TO ALL THE LAND INTERACTION...SO THE GFS LOOKS TOO DEEPWITH THE LOW. THE ECMWF HAS BASICALLY LOST THE FEATURE...AND HAS AFRONTAL BOUNDARY APPROACHING LATE MONDAY. WE CAN`T RULE OUT SOMESORT OF SYSTEM MOVING UP TOWARD THE GULF SINCE SO MANY INDEPENDENTMODELS HAVE LATCHED ON TO THE IDEA...BUT AT THE SAME TIME...WE ARETALKING ABOUT A FEATURE THAT DOESN`T EVEN EXIST YET...OTHER THAN AMASS OF CLOUDS SOUTH OF CENTRAL AMERICA. FOR NOW...I WILL ASSUMEANYTHING THAT DOES MOVE NORTH WILL BE SEVERELY IMPACTED BY CENTRALAMERICA AND EMERGE AS A VERY WEAK SYSTEM. THIS WOULD KEEP PRESSUREGRADIENTS ON THE WEAK SIDE...SO BEST BET SEEMS TO BE TO KEEP MAINEFFECTS OUT OF THE FORECAST AREA.

332. weatherblog 1:04 PM EDT on May 26, 2008 Hide this comment.Imagine if Alma forms in the EPAC, and it crosses over into the Atlantic Basin and mimicks Hurricane Alma with the same name (which seems a possible scenario as far as track goes and date goes).

LOL you stole my idea! I said that a few hours ago... It would be a rather rare occurrence wouldn't it

347. Weather456 5:22 PM GMT on May 26, 2008 I never saw so much dependency on computer models rather than evaluating the situation....most likely if an invest forms today or 2mr it would be 90E not 90L.

I'm not dependent on the computer models lol. I have been looking at the satellite loop and the water vapor imagery. Also some low level wind products.

Great observation 456. Maybe the games have begun sooner than expected. We will have to watch this area very closely during the next 24 to 48 hours. This area certainly looks quite intriguing. Just waiting to see how the tropical wave over Venezuela will interact with this new low.

It's one of the GFS's several ultimate tracks and intensities for this system...it's been swinging around a lot (just compare that image to the latest run). What really matters right now is that it's been consistently developing a system in the SW/West Caribbean and that the system's development has support from other models. I'd wait until we have an actual system (invest, TD, TS, whatever) to watch before determining intensity and eventual track.

I read a paper once before about how a Hurricane can cut down on the following years fire danger because it removes a lot of debris from the trees.

But could be responsible for a lot of fires in that first year. For about a year after Katrina, starting a few months afterward, we had a lot of fires in the forested areas of her impact. I still see the charred bark of those still standing along the highways to this day.

SE LA and Southern Mississippi are not usually prone to much in the way of fires. Simply a LOT of fuel laying about that wouldn't have been there without Katrina to make it so.

319. FLWeatherFreak91 4:59 PM GMT on May 26, 2008 Yes we do 0741.... Hurricanes do a lot of good as well as bad. I read a paper once before about how a Hurricane can cut down on the following years fire danger because it removes a lot of debris from the trees. Also, they take S. Fl out of drought but BAD if you live mobile home that were i live never wish hurr hit your area

Hey JFV. After finishing looking at the current conditions, models and projected synoptics next week, I do feel we will have an area of Low pressure develop. As for now, I am leaning more toward a CB solution rather than the EPAC. As for where it might head, it's a timing issue with the trough and the ridge parked over the SE CONUS. The NOGAPS wants to weaken the periphery considerably for a longer period of time, thus allowing the system to ride its western flank. The others are more toward the west with a stronger ridge.

Yes, certainly hope this pans out to give FL drought relief next week... IMHO, we'll have to see how the mid level ridging / troughing pattern over the CONUS / MX / W Atlantic evolves to determine the eventual track of the potential system once it begins it's NWD trek toward the Yucatan / S Gulf by weekend / early next week... A lot of the GFS runs indicated a blocking ridge will set up to the west over S / SW CONUS / MX, with a weakness (frontal trough) between that and Atlantic ridging that would allow a movement toward FL / N Gulf coast... On the other hand, some runs portrayed that ridge remaining well entrenched or redeveloping over the N Gulf / S CONUS (and perhaps weaker over S MX) along with weaker digging frontal trof (or none!) by that time frame and a more WWD building Atlantic ridge (or the CONUS ridge bridging across to it) that would block NWD motion / force a more westward movement once the feature lifts near Yucatan / or into S Gulf... Right now it remains a toss up... (LOL, as seen on today's 12Z GFS)... Quite a squeeze play between those ridges / trofs...

But in the meantime - As we're all concerned about possible negative impacts from tropical systems, let's keep our friends in Central America in mind... Whether it forms E Pac / W Carib or the low just lifts "up the gut" of Cen Am, that region could experience some very serious flooding / mudslide issues from hvy downpours for several days of such a prolonged event...

I haven't been convinced yet that anything will form, but for those of you who have been watching the GFS dont get discouraged by this one run. It has been consistent day to day for the last week, every now again a model will throw out a crazy run that doesn't make sense like this GFS run. you'll just have to wait for the next run to see if starts making more sense again.

Yes we do 0741.... Hurricanes do a lot of good as well as bad. I read a paper once before about how a Hurricane can cut down on the following years fire danger because it removes a lot of debris from the trees. Also, they take S. Fl out of drought.

ok, well maybe it will, i mean this model has been predicting a landfall in florida for like the past 3-6 days, now it predicting a landfall in Mexico..Drakeon you are right, the GFS is being a Drama Queen!

Wow I'm going to be disappointed if this storm doesn't materialize! The weather around here has been the most boring lately and plus I've spent countless hours starring at the screen trying to take in all this info. I hope the weather understands that all of us need something to do very badly lolwe donot need strong ts or hurr here in south fl!!!!!!!!!!

Discussion out of NWS Mobile...gives some good explaination of the upper dynamics of whats going on down there

LONG TERM (WEDNESDAY NIGHT THROUGH MONDAY)...

WAVENUMBER 5 GFS PROG SHOWS SOMEWHAT STRONG RIDGING OVER CUBA WHICHGOES THROUGH SEVERAL CYCLES OF BREAKING DOWN SLIGHTLY THENSTRENGTHENING AGAIN. EXPECT THE ROLE OF THIS FEATURE TO WORK AGAINSTCONVECTION IN THE OUTLOOK PERIOD. TRENDS FROM A REVIEW OF THE MEXGUIDANCE OVER THE LAST SEVERAL MODEL RUNS HAS BORNE THIS OUT WITHPOPS TRENDING OVERALL FROM CHANCE TO ISOLATED CATEGORIES IN DAYS 5TO 7 IN PROGRESSIVE MODEL RUNS. SMALL POPS BARELY IN DOUBLE DIGITSREMAIN AS A SURFACE HIGH OVER WESTLANT WILL BRING LIGHT ONSHORE FLOWTHROUGH SATURDAY.

WE HAVE BEEN EYEING THE PAST SEVERAL RUNS OF THE GFS AND ECMWF WHICHBRING A STRENGTHENING BAROTROPIC LOW OR OPEN WAVE INTO THE WESTERNCARIBBEAN NORTH OF THE YUCATAN PENINSULA THIS WEEKEND. HPC LONGRANGE DISCUSSIONS ALSO INDICATING CLOSE SCRUTINY THEREWITH. MODELSBUILDING AFOREMENTIONED WAVENUMBER 5 UPPER LEVEL RIDGING WITH LOWWIND SHEAR OVER CENTRAL AMERICA/WESTERN CARIBBEAN. POSITION OF FEATUREON HPC PROG CHARTS ARE STATED TO BE A MODEL AND ENSEMBLE OFLOCATIONAL AND PRESSURE AVERAGES. THERE SEEMS TO BE AN EQUAL CHANCETHIS COULD EVOLVE INTO A TUTT FEATURE...AS THERE IS A LOW SHOWN AT500 MB DIRECTLY OVER THE SURFACE FEATURE THIS WEEKEND. ALL SAID...ISSTILL UNCERTAIN AT THE MOMENT. 77/DALY